# HG changeset patch
# User Paul Boddie <paul@boddie.org.uk>
# Date 1508530880 -7200
# Node ID 4e16a443bb23f68685703b60fc0713a0fe08e84b
# Parent  f184dc45aadfa13a1951f1cb557192b93500ac8e
Introduced a dedicated function for creating rule-originating period instances.
Changed the fallback time zones used by RDATE and EXDATE period instances.

diff -r f184dc45aadf -r 4e16a443bb23 imiptools/data.py
--- a/imiptools/data.py	Wed Oct 18 00:57:40 2017 +0200
+++ b/imiptools/data.py	Fri Oct 20 22:21:20 2017 +0200
@@ -1089,6 +1089,24 @@
 
     return delegators
 
+def make_rule_period(start, duration, tzid, attr):
+
+    """
+    Make a period for the rule period starting at 'start' with the given
+    'duration' employing the given 'tzid' and datetime 'attr'.
+    """
+
+    # Determine the resolution of the period.
+
+    create = len(start) == 3 and date or datetime
+    start = to_timezone(create(*start), tzid)
+    end = start + duration
+
+    # Create the period with accompanying metadata based on the main
+    # period and event details.
+
+    return RecurringPeriod(start, end, tzid, "RRULE", attr)
+
 def get_periods(obj, tzid, start=None, end=None, inclusive=False):
 
     """
@@ -1134,7 +1152,7 @@
 
         until = parameters.get("UNTIL")
         if until:
-            until_dt = to_timezone(get_datetime(until, dtstart_attr), obj_tzid)
+            until_dt = to_timezone(get_datetime(until, dtstart_attr), obj_tzid or tzid)
             end = end and min(until_dt, end) or until_dt
             inclusive = True
 
@@ -1148,17 +1166,7 @@
         # done after the instances have been obtained.
 
         for recurrence_start in selector.materialise(dtstart, end, parameters.get("COUNT"), parameters.get("BYSETPOS"), inclusive):
-
-            # Determine the resolution of the period.
-
-            create = len(recurrence_start) == 3 and date or datetime
-            recurrence_start = to_timezone(create(*recurrence_start), obj_tzid)
-            recurrence_end = recurrence_start + main_period.get_duration()
-
-            # Create the period with accompanying metadata based on the main
-            # period and event details.
-
-            period = RecurringPeriod(recurrence_start, recurrence_end, tzid, "RRULE", dtstart_attr)
+            period = make_rule_period(recurrence_start, main_period.get_duration(), obj_tzid or tzid, dtstart_attr)
 
             # Filter out periods before the start.
 
@@ -1170,7 +1178,7 @@
 
     # Add recurrence dates.
 
-    rdates = obj.get_date_value_item_periods("RDATE", tzid)
+    rdates = obj.get_date_value_item_periods("RDATE", obj_tzid or tzid)
     if rdates:
         periods += rdates
 
@@ -1180,7 +1188,7 @@
 
     # Exclude exception dates.
 
-    exdates = obj.get_date_value_item_periods("EXDATE", tzid)
+    exdates = obj.get_date_value_item_periods("EXDATE", obj_tzid or tzid)
 
     if exdates:
         for period in exdates: